Recombinant DNA technology is used for production of heterologous proteins in various host microorganisms and animals including Escherichia coli (hereinafter referred to as E. coli). The target products are various biogenous proteins (herein, inclusive of polypeptides), and many of them have already been produced industrially for medical and other uses so far.
Among various hosts developed for production of heterologous proteins, yeasts seem favorable for expression of animal and plant proteins because of their eukaryotic similarity in the transcription and translation systems to animals and plants, and the baker's yeast (Saccharomyces cerevisiae) is a widely used host.
Among yeasts, S. pombe is known to be close to animal cells in nature as is evident from the fact that it grows by fission not by budding as a result of the different evolution process it has followed since it diverged from other yeasts at early stages. Therefore, the use of S. pombe as the host for expression of heterologous proteins is expected to provide a gene product closer to its natural form in animal cells.
Though studies of gene expression in S. pombe are delayed, the recent discovery of potent promoters functional in S. pombe has accelerated the development of expression systems using S. pombe as the host, and various improvements have been added to expression vectors to develop more stable and efficient expression systems (Patent Documents 1 to 8). As a result, expression systems using S. pombe as the host show high production efficiency now.
Production systems for heterologous proteins using eukaryotic microorganisms such as yeasts can be realized easily by conventional microbiological techniques and recombinant DNA technology with high productivity. Large cultures are already available and are acceleratingly used for actual production. Even after the scale is enlarged for actual production, cells retain the high production efficiency per cell obtained in the laboratory.
Considering that cost reduction is often demanded in actual production, it is necessary to improve the production efficiency of heterologous proteins through improvement in cell growth efficiency, suppression of degradation of the heterologous protein of interest, more efficient eukaryotic modifications in the microorganisms or more efficient utilization of the nutrition sources. For example, increase in the conversion of the carbon sources added to the medium for culture growth into the heterologous protein of interest is expected to drastically improve cell growth efficiency and therefore production efficiency of the heterologous protein, because efficient utilization of the carbon sources in the medium for production of the heterologous protein of interest seems to be sacrificed for their consumption by metabolic systems unnecessary for cell growth or production of the heterologous protein of interest (such as the ethanol fermentation system for production of ethanol).
Therefore, attempts have been made to improve production efficiency of heterologous proteins by a host by deleting or inactivating part or all of the genome of the host unnecessary or detrimental to production of heterologous proteins (Patent Documents 9 and 10).
The present inventors reported about the invention described in the patent applications from which the present application claims the earlier priority date, in an article published after the earlier priority application (before the later priority date) (Non-patent Document 1)    Patent Document 1: Japanese Patent No. 2776085    Patent Document 2: JP-A-07-163373    Patent Document 3: JP-A-10-215867    Patent Document 4: JP-A-10-234375    Patent Document 5: JP-A-11-192094    Patent Document 6: JP-A-2000-136199    Patent Document 7: JP-A-2000-262284    Patent Document 8: WO96/023890    Patent Document 9: WO02/101038    Patent Document 10: WO04/090117    Non-patent Document 1: Yeast, vol. 23, pp. 83-99, 2006